Traveling Light

A Swiss team of engineers has designed a plane that will fly around the world—without burning an ounce of fuel.

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WINGS OF DESIRE | Solar Impulse, show here soaring over the Alps, sets out on its first U.S. test flight, from San Francisco to New York, on May 1.
Courtesy of Solar Impulse

By

Finn-Olaf Jones

Updated April 28, 2013 11:35 p.m. ET

FOR BERTRAND PICCARD, the idea to build a solar-powered plane capable of circumnavigating the globe was hatched while running on empty. In March 1999, Piccard was on the final leg of an around-the-world journey by hot air balloon—the first-ever nonstop flight of its kind—when his Breitling Orbiter 3 swept low over the Egyptian desert and skidded to a halt on the corrugated plains. As Piccard stepped out onto the hot sand, he checked the fuel tanks mounted on his gondola and got a shock that became a defining moment. "We had left Switzerland with four tons of propane," he remembers. "We only had 40 kilos left! We almost didn't make it. I promised myself that next time I would fly around the world without using any fuel at all."

The 55-year-old Piccard, a trained psychiatrist with a confident, intense manner to match, is adept at making sure there is always a "next time"—no surprise, since he's descended from explorer royalty. His grandfather, Auguste, broke high altitude records in the '30s by designing a balloon with a pressurized cockpit, and later became the inspiration for Professor Calculus in the Tintin comics. In 1960, Piccard's father, Jacques, descended seven miles beneath the Pacific Ocean in another pressurized module to set a deep-dive record that has been matched only twice.

In 2003, Piccard approached European companies to sponsor what has become a $148 million project and began assembling a team of 80 engineers and technicians plucked largely from Swiss universities. After seven years of tinkering, they arrived at a machine with a deceptively simple design: Solar Impulse—with its sleek, clean lines, white-gloss finish and rakishly angled 208-foot wings (bent to increase the plane's stability)—resembles what you might get had Steve Jobs reimagined a child's balsa-wood glider in giant form.

"The crux to flying nonstop around the world with solar energy is being able to fly even when the sun isn't out, especially at night," notes André Borschberg, a former Swiss air force fighter ace and McKinsey & Company consultant who, as the project's CEO, oversees the design team and takes turns piloting the plane. The solution: Four specially developed lithium polymer batteries that store energy from the nearly 12,000 solar cells lining the horizontal stabilizer and the wings (cells that are supported by individual sponsorships at around $200 each—even former Vice President Al Gore bought one). During the daytime, the batteries accumulate energy while the plane climbs to a height of up to 30,000 feet. After sunset, the plane slowly glides to lower altitudes on the stored power until dawn, when the process starts again.

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Design specs for Solar Impulse's cockpit
Courtesy of Solar Impulse

THE MOST REVOLUTIONARY aspect of the plane's design are the materials used to minimize its weight. Every unneeded ounce had to be discarded so that the machine could bear the payload of even a single pilot. "We did a feasibility study and discovered that we weren't going to be able to get down to the right weight with any available construction materials," remembers Borschberg. "When we talked to aeronautics companies to see if they could develop this, everyone said it was impossible. So we turned to a boat-building company."

The company—Decision SA boatyards, which specializes in racing ships out of Ecublens, Switzerland—created rectangular carbon-fiber beams, honeycombed to lighten the plane's internal structure. Over this skeleton they pulled a specially developed carbon skin half the weight of copy machine paper. "You can actually tear the plane's skin apart with your hands," says Piccard. "It's funny something so strong on a grand scale is so delicate up close." Though Solar Impulse is as wide as a
Boeing
747, it weighs a mere 3,500 pounds—about as much as a family sedan. But unlike a car, Solar Impulse can be disassembled into 10 pieces and packed into a plane's hull for shipment anywhere in the world.

In the past three years the plane has flown 64 test flights throughout Europe and North Africa in preparation for an around-the-world odyssey, and on May 1 it will set out on its first test flight in the Americas, which will make several stops from San Francisco to New York, over the course of many weeks.

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THE RIGHT STUFF | Bertrand Piccard, right, and Andre Borschberg will take turns piloting Solar Impulse.
Courtesy of Solar Impulse

Borschberg and Piccard will again take turns piloting a second version of Solar Impulse being developed from the current prototype for an around-the-world voyage planned for 2015, with half a dozen stops. "The old design has worked well," notes Piccard. "The new Solar Impulse's changes will be mostly internal, especially the cockpit."

Few watching the test flights would describe Solar Impulse as elegant, as it lumbers across the runway at an improbably low speed. But within a mere 500 feet, a remarkable transformation takes place: The immense contraption takes off surprisingly quick, thanks to its deceptively light weight. Once airborne, Solar Impulse becomes a natural creature of the wind, flying smoothly at an average of 43 mph. The perfect silence of the sky is broken only by the propellers' steady whirr. "There's not even a vibration," says Piccard. "In calm weather I can steer it with two fingers."

While the prototype has only flown up to 26 hours at a time, the new one will need to fly for much longer durations—up to 120 hours—to overcome oceans and other terrain. Modifications include an airtight cockpit, a fully reclining seat to allow the pilot to nap and a toilet under the seat. As Piccard gently explains, the current improvised setup involves "full drinking bottle on right, empty bottle on left at takeoff. Empty bottle on right, full bottle on left at landing."

Perhaps the most innovative addition will be the addition of an autopilot. "We have created a sort of black box that will wake the pilot up if something is wrong," says Borschberg. "We will also have sensors around our arms which will vibrate when the plane banks too far to the left or right. It's the first time an autopilot system will use touch to alert the pilot."

Although this feature allows the pilot to rest for an extended period during flight, Piccard hopes to minimize that part. "Solar Impulse isn't a place to sleep. It's a place to stay calm." For Piccard, who is trained in the art of hypnosis—and who put his Breitling copilot into a trance as they crossed the Atlantic—this means creating a self-induced hypnotic state. "I am relying on my skills to keep my head utterly relaxed and alert while the body rests." Borschberg's plan for flying solo long-term is more simple: "I will do yoga."

Although no one knows for sure how Solar Impulse's around-the-world trip will alter the future of aviation, its innovative technologies are already being applied in other fields. "Not only will the batteries we developed be on the market soon," says Borschberg, "but the foam used to insulate them will be used on refrigerators to save 10 to 15 percent in energy loss."

"With a record-setting attempt like the Solar Impulse flight, the practical part is not particularly apparent," says legendary plane designer and test pilot Jon Karkow, chief engineer for Richard Branson and Steve Fossett's GlobalFlyer, which flew around the world in 2005 on a single tank of gas. "When you look back at history you'll see that these leaps into new technologies might at first not look interesting, but an electric airplane like Solar Impulse will have trickle-down effects," Karkos adds. "Especially when you remember that we won't always have petroleum—but we'll always want to fly."

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